Albertosaurus Life History

This week's paper (cited below) describes the construction of a life history table for Albertosaurus sarcophagus. The life table was constructed using an attritional assemblage from Dinosaur Provincial Park in Alberta. From this assemblage the authors were able to estimate mortality rates among the different age classes as well as the life expectancy. Most notably, the survivorship curve was found to be sigmoidal with a midlife decline in survivorship. The A. sarcophagus juveniles appear to have experienced high mortality rates followed by a decline in mortality with age (and increase in size). Mortality rates remained constant until the onset of breeding, suggesting that large clutches of young were adaptive for a short reproductive life span. The study confirmed the results of a previous study and increased the statistical power.

I find it interesting that these types of tables can be drawn for extinct organisms but I don't think it is surprising to find that a large animal such as Albertosaurus share similar life history traits to other large vertebrates. It is interesting, however, that the same patterns are not seen in any extant reptilian. This begs the question of whether the apparent differences in metabolism between extant lizards (for example) and large terrestrial dinosaurs (which are at least inertial homeotherms) are the reason for life history differences. It is difficult to rule out other factors such as habitat, body size, and clutch size, however. But I do wish there was a citation in the paper on extant reptilian life history tables and survivorship curves. How do reptiles differ from similarly sized mammals etc? does it change with body size? The paper may have been strengthened by further background on life tables and survivorship curves as well as direct comparison to some living representatives.